infidelity, disloyalty, deceit, and betrayal are acts of ungodliness not pleasing to God.
Surely as a wife treacherously departeth from her husband, so have ye dealt treacherously with me, O house of Israel, saith the LORD. A voice was heard upon the high places, weeping and supplications of the children of Israel: for they have perverted their way, and they have forgotten the LORD their God. Return, ye backsliding children, and I will heal your backslidings. Behold, we come unto thee; for thou art the LORD our God. (Jeremiah 3:20-22 KJV)
These scripture verses use an analogy of a wife leaving her husband choosing to commit adultery and comparing it with the spiritual adultery of the Jewish people against the faithfulness of God. In both cases, whether it be a marriage of a man and wife or having a personal relationship with God; infidelity, disloyalty, deceit, and betrayal are acts of ungodliness not pleasing to a righteous God.
Not only was this applicable for the Jewish people but applies in our lives today:
Adultery is a physical act or mental assent committed contrary to having a close relationship with one’s own spouse and God.
Spiritual adultery is an act that is committed directly against, or in opposition to, the authority and holiness of God. Both are selfish plunges into flagrant sin greatly affecting our relationship with God and others.
In our lives we are either enjoying a close knit personal spiritual relationship with God or we are headed backwards committing spiritual adultery and existing away from the holiness and righteousness of God aligned with the darkness of the god of this world.